A ring binder is applied to secure loose leaves, such as punched paper, into a file folder or a notebook. It is characterized by ring elements for securing paper, wherein the ring elements can be opened optionally to add or remove paper, or closed to secure paper, while allowing paper to move along them. Generally a lever is provided on both ends of the binder to move the ring elements between an opened position and a closed position.
FIGS. 20 and 21 show a ring binder according to the prior art. In the conventional ring binder, end faces 56 of half ring elements 54 form an engagement configuration with a convex portion and a concave portion. When the end faces 56 of the two half ring elements 54 close, the convex portion of the end face 56 of one half ring element engages with the concave portion of the end face 56 of the other half ring element. One disadvantage of this type of engagement configuration is that the end faces can not close tightly and align to each other exactly when two half ring elements close, so that vertical and transverse misalignments for the engagement configuration will occur, as illustrated in FIGS. 20 and 21. Owing to the disadvantage that the end faces 56 of the binder which engage with each other misalign up and down, paper which is bound by the binder can not be turned over smoothly, and can even be torn.